An output power of an engine of a handheld engine-driven working machine, such as a chain saw, varies due to variations of a carburetor and an engine and usage circumstances (for example, a temperature, an atmospheric pressure, a moisture, and a kind of fuel). In order to operate the engine at a predetermined designed output power (predetermined air-fuel ratio), the handheld engine-driven working machine having an electronically controlled carburetor has been known, and such a carburetor has a solenoid valve for adjusting an amount of supplying fuel into the carburetor (for example, see the Patent Publication 1). By changing a control value corresponding to an opening degree of the solenoid valve to adjust the amount of supplying fuel into the carburetor, the handheld engine-driven working machine can be operated at the predetermined designed output power.
Manufacturers of the handheld engine-driven working machines perform an operation with non-load (a completion operation) of the handheld engine-driven working machine before shipping it, and provisionally determine the above-stated control value for operating the engine at the designed output power (a control value for completion operation V0). On the other hand, after shipping the handheld engine-driven working machine, a circumstance in which the handheld engine-driven working machine is actually used is different from a circumstance in which the completion operation is performed, and for example, a temperature, an atmosphere pressure, and a kind of fuel may vary. For this reason, in an operation under the usage circumstance (an actual operation), the above-stated control value for operating the engine at the designed output power (an actual operation control value) is different from the control value for completion operation V0. Thus, it is advantage that the actual operation control value is determined in the actual operation.
The Patent Publication 1 describes a handheld engine-driven working machine which automatically determines the actual operation control value. Briefly, the handheld engine-driven working machine is operated with non-load under a usage circumstance, and a PI control for a control value corresponding to an opening degree of the solenoid valve is performed so that a rotating speed of the engine when a throttle is fully opened becomes a target rotating speed. In the PI control, a PI calculation is performed by using a difference between a current rotating speed and the target rotating speed and the control value is increased or decreased by a result of the PI calculation.
Specifically, after starting the engine, when the engine rotating speed is out of a predetermined engine rotating speed range, the PI control is not performed, and when the engine rotating speed is within the predetermined engine rotating speed range, the PI control is performed. Further, when the engine rotating speed is lower than the target rotating speed, the control value of the solenoid valve is varied so that the opening degree of the solenoid valve becomes smaller to make a fuel consumption lean, and when the rotating speed of the engine is higher than the target rotating speed, the control value of the solenoid valve is varied so that the opening degree of the solenoid valve becomes larger to make the fuel consumption rich. During a fixed number of continuous rotations, if the engine rotating speed is within a predetermined permissible range and the number of times of control implementations reaches a predetermined number of times, the PI control is finished and the control value at the finishing is determined as the actual operation control value.
FIG. 5 is a graph showing changes in the engine rotating speed and the control value with respect to time around a time when the actual operation control value was determined in an example where the actual operation of the chain saw with non load was performed while the control described in the Patent Publication 1 was performed. In this connection, the control value corresponding to the opening degree of the solenoid valve was determined so as to linearly change between 0 per mill (permillage) at a fully-opened solenoid valve and 1000 per mill at a fully-closed solenoid valve. Further, after starting the engine, the rotating speed of the engine was calculated per one rotation of the engine. Further, a racing operation was performed, in which an operation of fully opening the throttle for a several seconds and an operation of fully closing the throttle for a several seconds were alternately repeated.
In FIG. 5, after starting the engine, when the engine rotating speed was out of the predetermined rotating speed range (11000-14000 rpm) (A5), the PI control was not performed, and when it was within the predetermined rotating speed range (11000-14000 rpm) (B51, B52), the PI control was performed (C53). Further, when the rotating speed of the engine was within a range lower than the target rotating speed (12000 rpm) (B51), the control value was increased so that the opening degree of the solenoid valve was decreased to make the fuel consumption lean (C54), and when the rotating speed of the engine was within a range higher than the target rotating speed (12000 rpm) (B52), the control value was decreased so that the opening degree of the solenoid valve was increased to make the fuel consumption rich (C55). During a predetermined number of times of continuous rotations (for example, 5000 times), when the engine rotating speed was within a predetermined range (for example, 11500-12500 rpm) and the control value did not become changing (C56), the PI control was finished and the control value at the finishing was determined as the actual operation control value. Concretely, in the third operation shown in FIG. 5, during 5000 rotations, when the engine rotating speed was within the predetermined range (12000±500 rpm) and the number of times of the control implementations reached a predetermined number of times (30 times) (C56), the PI control was finished (C53′) and the control value at the finishing was determined as the actual operation control value.
In the example shown in FIG. 5, when the throttle was fully opened, the engine rotating speed was increased to approximate 12000 rpm substantially without overshooting (C51). When the throttle was returned, the engine rotating speed was decreased to an idling rotating speed (C52). The fluctuation of the engine rotating speed was relatively small after the engine rotating speed was increased.
In this connection, a control value determined by manufacturers of the handheld engine-driven working machines in the above-stated way before shipping is the control value for completion operation and is used as a basic value.